Continuous casting has long been one of the more active areas of innovation in the metallurgical field and as a result a relatively large volume of patent and other technical literature has developed and continues to grow pertaining to the art of continuous casting. For a variety of reasons, however, comparatively very few of the concepts set out in the voluminous prior art have materialized in commercial form. The continuous casting systems for metal that have reached such status have usually involved the use of some type of mechanical contacting mold to contact, contain and shape the molten metal while it is solidifying. These molds take the form of casting wheels and casting belts and may in the case of the so-called "dip-forming" process take the form of seed rod which is in effect an internal mold.
As will be developed in more detail below, the present invention involves as a central feature the use of an alternating electromagnetic levitation field to support and contain out of continuous contact with the containing surface of a casting vessel an upwardly moving column of molten metal and eliminates the necessity for the casting wheel, the casting belt, the seed rod or other contacting molds now used in the industry. In addition to simplifying the continuous casting of metals forming and other commercial production systems, the apparatus of this invention opens the opportunity of making small to moderate quantities of copper, brass, nickle and other metallic rods by continuous casting instead of by the more expensive billet casting and hot rolling processes presently in general use.
With generally the same objectives in view, others have proposed the use of an electromagnetic mold to contain a metal melt pool on top of a downwardly moving ingot while the outer lateral portions of the pool are being solidified. This general departure is described in U.S. Pat. No. 3,467,166 (Getselev, et al) and is further developed in U.S. Pat. No. 3,605,865 (Getselev); U.S. Pat. No. 3,735,799 (Karlson); U.S. Pat. No. 4,014,379 (Getselev); and U.S. Pat. No. 4,126,175 (Getselev). In each instance, accretion is longitudinal, melt being delivered semi-continuously or continuously by gravity flow on the upper end of the descending ingot. One of the more serious drawbacks of this approach is the fact that the "fail safe" characteristic of casting upwardly is absent. Thus, in the event of an unexpected electric power failure, molten metal will spill out of the downward casting apparatus instead of merely running back, as in this invention, into the holding vessel. In addition, the melt overflow and breakout possibilities in downward casting require constant careful control of both the melt feed rate and the ingot removal rate. Moreover, these rates are drastically limited by a heat exchange problem which consequently diminishes the commercial potential of this special type of continuous casting.
According to another recent departure described in U.S. Pat. Nos. 3,746,077 (Lohikoski, et al) and 3,872,913 (Lohikoski) assigned to Outokumpo Oy, molten metal is either hydrostatically forced or pulled by vacuum upwardly into an open-ended, vertically-disposed mechanical mold as freshly-formed and cooled cast product is discontinuously and intermittently removed from physical contact with the upper end of the mechanical mold which contains the molten metal. In this way, the fail-safe feature is gained but only by accepting the major shortcomings of the external contact mold.
In Japanese patent application No. 5413/1973 published Feb. 16, 1973, Kenji Chijiiwa--Inventor, a continuous casting method and system is disclosed in which molten metal is supposed to be drawn upwards (lifted) from its reservoir by means of an electromagnetic pump. In this system the electromagnetic pump alledgedly is employed as an element in an overall feedback control system for regulating the rate of production of cast metal by continuously adjusting the pumping rate of the electromagnetic pump. The system has not been used commercially since its conception in September, 1970.